火焰辐射及偶丝导热对热电偶测温影响的数值分析

本文利用层流同向扩散乙烯火焰的数值模拟结果,根据所得的火焰温度场、气体速度场、火焰辐射场,分析火焰辐射、热电偶偶丝导热对热电偶测温的影响.结果表明在火焰的低温区火焰辐射要大于节点向外辐射,节点得到的能量要高于节点损失的能量,因此在火焰的低温区节点温度要高于当地的气体温度;同时直径为100μm的热电偶存在较大的导热,对节点温度测量有较大的影响.     

Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.     

Use of elemental size distributions in identifying particle formation modes

The chemical composition of particles generated during pulverized coal combustion is the consequence of their formation processes. This work aims to use the size resolved elemental composition of coal-derived particles to identify their formation modes. A size-classified bituminous coal is burnt in a laboratory drop tube furnace at 1150, 1250, and 1350 °C, respectively. The elemental composition of the size-segregated particles from coal combustion is analyzed and the total mass fraction size distributions of Si and Al are obtained. Three particle formation modes are observed in these distribution profiles. The coarse mode has the highest value of the total mass fraction of Si and Al while the ultrafine mode has the lowest one. The total mass fraction of Si and Al in these two modes is nearly independent of particle size. It is believed that the coarse mode is formed by the mineral coalescence mechanism and the ultrafine mode by the vaporization–condensation mechanism. The difference in the total mass fraction of Si and Al between the central mode and the other two indicates that the central mode is formed by different mechanisms. Based on the observation that the total mass fraction of Si and Al in this mode increases with increasing particle size, heterogeneous condensation of vaporized species on existing fine residual ash particles is proposed to account for the formation of these particles. The study of the elemental composition of the three modes represented in five categories verifies the proposed formation mechanisms for them to some extent.     

GaN MOS-HEMT Using Ultra-Thin A1203 Dielectric Grown by Atomic Layer Deposition

We report a GaN metal-oxide-semiconductor high electron mobility transistor （MOS-HEMT） with atomic layer deposited （ALD） Al2O3 gate dielectric. Based on the previous work [Appl. Phys. Lett. 86 （2005） 063501] of Ye et al. by decreasing the thickness of the gate oxide to 3.5nm and optimizing the device fabrication process, the device with maximum transconductance of 150mS/mm is produced and discussed in comparison with the result of lOOmS/mm of Ye et al. The corresponding drain current density in the 0.8-μm-gate-length MOS-HEMT is 800mA/mm at the gate bias of 3.0 V. The gate leakage is two orders of magnitude lower than that of the conventional A1GaN/GaN HEMT. The excellent characteristics of this novel MOS-HEMT device structure with ALD Al2O3 gate dielectric are presented.     

Near-Field Fluorescence and Topography Characterization of a Single Nanometre Fluorophore by Apertureless Tip-Enhanced Scanning Near-Field Microscopy

Tip-enhanced near-field fluorescence and topography characterization of a single nanometre fluorophore is conducted by using an apertureless scanning near-field microscopy system. A fluorophore with size 80hm is mapped with a spatial resolution of 10hm. The corresponding near-field fluorescence data shows significant signal enhancement due to the apertureless tip-enhanced effect. With the nanometre spatial resolution capability and nanometre local tip-enhanced effect, the apertureless tip-enhanced scanning near-field microscopy may be further used to characterize a single molecule by realizing the local near-field spectrum assignment corresponding to topography at nanometre scale.     

Phase-locking observed among high-order lateral modes of a broad-stripe diode array inside an external cavity

For a laser diode array (LDA) positioned in an external cavity of a certain length, a very strong inter-emitter coupling can be established between the off-axis lateral modes of the broad-stripe emitters. Under these circumstances, the phase-locked operation of the LDA due to couplings between off-axis modes of emitters has been observed, for the first time to our knowledge. The observations suggest that phase locking of a broad-stripe LDA can be achieved among different emitter lateral modes by selecting different cavity lengths.     

基于梯度矢量流和主动轮廓模型的海陆边界提取

利用边缘检测与主动轮廓模型组合的方法可提取海陆边界线,但易受轮廓跟踪的缺点影响.在该方法的基础上,利用边缘检测与梯度矢量流的有向力作用生成初始轮廓线,再使用主动轮廓模型对初始轮廓线进行调整,得到精确的海陆边界.实验证明该方法可简便地生成有效的初始轮廓线并准确提取海陆边界,避免使用轮廓跟踪法.该方法可利用GIS数据辅助以简化提取流程.     

Size‐Mediated Recurring Spinel Sub‐nanodomains in Li‐ and Mn‐Rich Layered Cathode Materials

Li‐ and Mn‐rich layered oxides are among the most promising cathode materials for Li‐ion batteries with high theoretical energy density. Its practical application is, however, hampered by the capacity and voltage fade after long cycling. Herein, a finite difference method for near‐edge structure (FDMNES) code was combined with in situ X‐ray absorption spectroscopy (XAS) and transmission electron microscopy/electron energy loss spectroscopy (TEM/EELS) to investigate the evolution of transition metals (TMs) in fresh and heavily cycled electrodes. Theoretical modeling reveals a recurring partially reversible LiMn₂O₄‐like sub‐nanodomain formation/dissolution process during each charge/discharge, which accumulates gradually and accounts for the Mn phase transition. From the modeling of spectra and maps of the valence state over large regions of the cathodes, it was found that the phase change is size‐dependent. After prolonged cycling, the TMs displayed different levels of inactivity.     

One-Pot Facile Synthesis of Noble Metal Nanoparticles Supported on rGO with Enhanced Catalytic Performance for 4-Nitrophenol Reduction

In this study, reduced graphene oxide (rGO)-supported noble metal (gold, silver, and platinum) nanoparticle catalysts were prepared via the one-pot facile co-reduction technique. Various measurement techniques were used to investigate the structures and properties of the catalysts. The relative intensity ratios of I_D/I_G in rGO/Au, rGO/Ag, rGO/Pt, and GO were 1.106, 1.078, 1.047, and 0.863, respectively. The results showed the formation of rGO and that noble metal nanoparticles were decorated on rGO. Furthermore, the catalytic activities of the designed nanocomposites were investigated via 4-nitrophenol. The catalysts were used in 4-nitrophenol reduction. The catalytic performance of the catalysts was evaluated using the apparent rate constant k values. The k value of rGO/Au was 0.618 min⁻¹, which was higher than those of rGO/Ag (0.55 min⁻¹) and rGO/Pt (0.038 min⁻¹). The result proved that the rGO/Au catalyst exhibited a higher catalytic performance than the rGO/Ag catalyst and the rGO/Pt catalyst. The results provide a facile method for the synthesis of rGO-supported nanomaterials in catalysis.     

2-酯基-1,5-苯并氧氮杂的合成及反应副产物的研究

以取代苯、丁烯二酸酐、邻氨基(对氯邻氨基)苯酚为原料,合成了一系列2-酯基-1,5-苯并氧氮杂衍生物,其结构通过IR,1H NMR,MS(HRMS)及元素分析进行表征.同时,确定了一个主要副产物2-苯甲酰甲基-2H-1,4-苯并噁嗪-3(4H)-酮(6h’)的结构,提出了其可能的生成机理.研究还表明,中间体4-芳基-4-氧代-2-丁烯酸酯(4)在对甲基苯磺酸为催化剂、DMF作溶剂、回流温度下反应时主要生成目标产物2-酯基-1,5-苯并氧氮杂6,而在冰醋酸为催化剂、甲醇作溶剂、回流温度下反应时则主要生成副产物6h’.